Techniques for feedback control of the output voltage in galvanically-isolated switching power converters has traditionally required use of auxiliary transformer windings or opto-isolators to sense the output voltage across the galvanic isolation boundary. Primary-side sampled feedback circuits using auxiliary windings in fly-back power converters are shown for example in Ball et al., Circuit and Method for a Switching Power Supply with Primary Side Transformer Sensing, U.S. Pat. No. 6,333,624; Bonte et al., Switching Regulator Circuit Using Magnetic Flux-Sensing, U.S. Pat. No. 5,305,192; Bonte et al., Switching Regulator Circuit Using Magnetic Flux-Sensing, U.S. Pat. No. 5,438,499; Majid et al., Sample-and-Hold Circuit for a Switched-Mode Power Supply, U.S. Pat. No. 5,874,841; Telefus et al., Power Converters with Primary-Only Feedback, publication no. US 2003/0132739 A1 published Jul. 17, 2003; Yang et al, Primary-Side Regulated Pulse Width Modulation Controller with Improved Load Regulation, publication no. US 2004/0257839 A1, published Dec. 23, 2004. Similarly, a converter sampling a voltage across the primary winding is shown in Thomas, Transformer-Coupled Power Converter Sampling System, U.S. Pat. No. 3,764,881.